Transcriptional Response of Yeast to Aflatoxin B₁: Recombinational Repair InvolvingRAD51andRAD1

Abstract

The potent carcinogen aflatoxin B 1 is a weak mutagen but a strong recombinagen in Saccharomyces cerevisiae. Aflatoxin B 1 exposure greatly increases frequencies of both heteroallelic recombination and chromosomal translocations. We analyzed the gene expression pattern of diploid cells exposed to aflatoxin B 1 using high-density oligonucleotide arrays comprising specific probes for all 6218 open reading frames. Among 183 responsive genes, 46 are involved in either DNA repair or in control of cell growth and division. Inducible growth control genes include those in the TOR signaling pathway and SPO12, whereas PKC1 is downregulated. Eleven of the 15 inducible DNA repair genes, including RAD51, participate in recombination. Survival and translocation frequencies are reduced in the rad51 diploid after aflatoxin B 1 exposure. In mec1 checkpoint mutants, aflatoxin B 1 exposure does not induce RAD51 expression or increase translocation frequencies; however, when RAD51 is constitutively overexpressed in the mec1 mutant, aflatoxin B 1 exposure increased translocation frequencies. Thus the transcriptional profile after aflatoxin B 1 exposure may elucidate the genotoxic properties of aflatoxin B 1 .

Expression of a Human Cytochrome P450 in Yeast Permits Analysis of Pathways for Response to and Repair of Aflatoxin-Induced DNA Damage

“…3) also suggests that both NER and HRR act on one or more common substrates. These results are consistent with the involvement of Rad1, required in NER (81), in the repair of AFB 1 -induced DNA damage via recombinational repair (48). In the absence of the two repair pathways, these AFB 1 -induced DNA lesions are channeled into a mutagenic repair pathway mediated by REV3.…”

“…Both pathways are also involved in the repair of UV damage (8). Our data are also consistent with the loss of AFB 1 -induced recombination in a diploid rad51 mutant transformed with human CYP1A1 (48). It could be that replication forks collapse when encountering AFB 1 -DNA adducts, leaving single strands whose repair is likely to be dependent on Rad51 (19).…”

“…Early studies indicated that AFB 1 is strongly recombinogenic but only weakly mutagenic in yeast (87). Our work offers an explanation of these observations, in that wild-type cells readily and faithfully repair AFB 1 -induced damage using homologous recombination and nucleotide excision repair, consistent with the role of recombinational repair in the repair of AFB 1 -induced DNA damage in another study (48). Our data suggest that, in the absence of these pathways, the mutagenesis that ensues is via the error-prone translesion synthesis pathway and requires a functional DNA damage checkpoint.…”

In-depth analyses unveil the association and possible functional involvement of novel RAD51B polymorphisms in age-related macular degeneration

“…The expression of the RAD1 gene, the product of which plays a crucial role in the repair of DNA double-strand breaks by homologous recombination, was shown to be downregulated in response to oxidative stimulus in AMD patients (Strunnikova et al 2005). The coordinated involvement of Rad51 and Rad1 in recombinational repair of DNA damage implicates the potential role of RAD51-dependent DNA repair in circumstances of elevated oxidative reaction species (Keller-Seitz et al 2004).…”

Yeast as a Humanized Model Organism for Biotransformation-Related Toxicity

“…Several of these pathways are also involved in tolerance to aflatoxin B 1 in mammalian cells [9]. Additionally, microarray experiments on aflatoxin B 1 treated yeast cells expressing CYP1A2 showed that expression of genes involved in DNA synthesis and repair, cell cycle regulation, or protein degradation and synthesis was significantly altered [25,130].…”